Hopefully in the DLC we get something more involving Gym Leaders/E4/maybe even Team Star Leaders
I'd be surprised and disappointed if they didn't. While SwSh had you able to rematch the Gym Leaders in the base game already, they did later on add in the Galarian Star Tournament which was fun. I know GF is adverse to using good ideas again, though I hope maybe them leaving out E4 Rematches (and Gym Leaders rematches) would mean they're planning something like it to go along with the DLCs.
Yes, I said, "go along with the DLCs". Not PART of the DLC, along with. For free to everyone. GF, you for some reason want more time or wait to have the League rematches, fine I guess, I guess it gives another reason for players to come back to the games. But don't you DARE put basic rematches as part of the paid DLC. You want to have something like a Paldean Star Tournament part of the DLC? Fine, go right ahead, that's technically an additional feature which would hopefully also come along with some unique stuff such as additional rewards and interactions between characters. But there should be no reason why a player can't go to the Gym (Building) or the Pokemon League and ask to challenge the Gym Leader/Elite Four again but this time at higher levels.
Oddly the Team Flare bosses you can fight again (once a day, but don't think you'd want to do more than that). You can't rematch their Starmobiles though. And of course the Titans are one-and-done.
If it were up to me, alongside Teal Mask I'd have an free DLC which lets you re-challenge the bosses of each of the three Treasure Hunt storylines: League (Gym Leaders, Elite Four, Geeta, & Nemona), Team Star (the Starmobile battles & Penny), and the Titans (also able to battle Arven too). Nothing too special, just able to re-experience those battles but at higher Levels.
Then, for the Indigo Disk, since it's about you visiting another Academy, I can see them using that to do a Paldean Star League thing. Teal Mask had the basic rematches alongside it, now it's time to do some more ambitious things. Maybe add in more Titans (actually they could probably do this in the Teal Mask too, there was only 5 Types covered by the Titans leaving 13 available), and give Penny a Starmobile.





